通过比较两个文档的字段值来定义Firestore查询 [英] Defining a Firestore query by comparing two document's fields values

问题描述

我正在Cloud Firestore上迈出第一步，而我被困在这一步上.我正在寻找一个where查询，以返回限制为> = 的值.

I'm having my first steps with Cloud Firestore, and I am stuck on this one. I'm looking for a where query to return me values that are >= the limit.

  [{
    'limit': 100,
    'value': 200 
  }, 
  {
    'limit': 50,
    'value: 50,
  },
  {
    'limit': 95,
    'value': 90, 
  }]

我正在Cloud Function中使用Firebase Admin Python SDK.

I am using the Firebase Admin Python SDK in a Cloud Function.

有任何提示吗?

推荐答案

如Alex所述，在使用Firestore执行查询时，无法比较两个文档的字段值.

As Alex has explained, there is no way to compare two document's fields values when executing a query with Firestore.

一种可能的方法是将文档保存到数据库时保存不等式的结果.如果在保存检查"文档时知道两个值( limit 和 value )，则可以添加第三个字段，例如， valueAboveLimit的值为 True 或 False ，该值是您在保存检查"文档时(即从前端使用相应的客户端SDK或从具有Firebase Admin Python SDK的服务器上获取，具体取决于您编写Firestore文档的方式).

One possible approach, would be to save the result of the inequality when you save the document to the database. If, when you save a "check" document you know the two values (limit and value), you could add a third field named, for instance,valueAboveLimit with a value of True or False, that you calculate when you save the "check" document (i.e. from your front-end with the corresponding client SDK or from a server with the Firebase Admin Python SDK, depending on how you write the Firestore documents).

然后您的查询将很容易:

Then your query will be easy:

database = firestore.client()
col_checks = database.collection('checks')
query_checks = col_checks.where('valueAboveLimit', '==', True)
results = query_checks.get()

---

如果在保存Firestore文档时没有 limit 和 value 的值(例如 limit 字段是在稍后编写的)，您可以使用触发

---

In case you don't have the values of limit and value at the time you save the Firestore document (for example the limit field is written later), you could use a Cloud Function that is triggered when the Firestore document is changed and, if the two fields are present, calculates and saves this valueAboveLimit field.

这篇关于通过比较两个文档的字段值来定义Firestore查询的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！